1. Field of the Invention
The present invention relates to an ophthalmometric apparatus, such as a noncontact intraocular pressure measuring apparatus or an objective ophthalmometer, and, more specifically, to an optical alignment system for an ophthalmometric apparatus.
2. Description of the Related Art
When examining the eyeball with an ophthalmometric apparatus, such as a noncontact intraocular pressure measuring apparatus or an objective ophthalmometer, the vertical and horizontal positions of the ophthalmometric apparatus relative to the eye and the operating distance between the ophthalmometric apparatus and the eye must be adjusted for alignment.
The applicant of the present patent application proposed previously a novel alignment adjusting system for an ophthalmometric apparatus in Japanese Patent Application No. Hei 4-122562 (Title of the invention: Ophthalmometer). An optical system described as a preferred embodiment of the invention in the specification comprises a first optical index detector that forms a" position index for the adjustment of the vertical and horizontal positions of the measuring system, projects the index and detects the same, and a second optical index detector that forms a distance index, projects an alignment light beam obliquely, and receives the alignment light beam at a position in mirror image relation with the position from which the alignment light beam is projected. A graphic mark (distance mark) represented by the output of the second index detector is displayed on a monitor display to provide information for adjustment.
In this previously proposed optical system, the accuracy of the detecting operation of the second index detector is affected delicately by the horizontal position of the eye relative to the second index detector, and the data acquired by the second index detector includes errors unless the horizontal position of the eye relative to the second index detector is adjusted accurately.
Furthermore, since the eye never remains stationary and keeps slight movement, the vertical and horizontal positions of the eye relative to the second index detector may change during the adjustment of the operating distance after the adjustment of the vertical and horizontal positions of the eye. In such a case, the adjustment of the vertical and horizontal positions of the eye relative to the second index detector must be carried out again. Thus, the previously proposed optical system requires a very troublesome operation.